Certain types of integrated circuit are protected by coating the surface of the device with a passivation layer of silicon carbide (SiC). Bond pads of a conductive metal, generally aluminum, are formed on the integrated circuit in openings in the SiC passivation layer. Although aluminum forms a good ohmic contact to the integrated circuit, it must be protected from oxidation which could adversely affect its conductivity. The aluminum bond pads are generally protected by a layer of gold (Au) which is coated over the bond pads. The gold is non-corrosive with respect to oxygen and is a good conductor. However, there is a problem of providing gold over aluminum. Therefore, a barrier layer is generally provided between the aluminum bond pad and the gold layer. One barrier material used in titanium-tungsten (TiW).
In making the contacts for the integrated circuit, a layer of the TiW barrier layer is deposited over the aluminum bond pads and the SiC passivation layer, and a layer of gold is deposited over the barrier layer. The gold layer is then defined to form the contact using standard photolithographic techniques and etching. Etching the gold layer to define the contacts exposes a portion of the underlying TiW barrier layer. The exposed portion of the TiW barrier layer is then etched away to form the final contact. A problem in defining the TiW barrier layer is to use an etchant which does not attack the interface between the TiW barrier layer and the SiC passivation layer, or at least does not excessively attack the interface. If such attack occurs, the TiW would undercut the gold layer thereby compromising the barrier metal integrity that protects the aluminum bond pad. Therefore, it is desirable to have an etchant which will etch the TiW barrier layer but will not attack, or excessively attack, the interface between the TiW barrier layer and the SiC passivation layer.